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* Detect infinite loops using blackholing.

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This commit is contained in:
Eelco Dolstra 2003-08-14 12:37:31 +00:00
parent 2e16ff22ac
commit dc0ef2ca98
2 changed files with 14 additions and 3 deletions
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16
src/fix.cc
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@ -18,6 +18,13 @@ struct EvalState
NormalForms normalForms;
PkgPaths pkgPaths;
PkgHashes pkgHashes; /* normalised package hashes */
Expr blackHole;
EvalState()
{
blackHole = ATmake("BlackHole()");
if (!blackHole) throw Error("cannot build black hole");
}
};
@ -64,8 +71,6 @@ static Expr substExpr(string x, Expr rep, Expr e)
}
}
/* ??? unfair substitutions? */
/* Generically substitute in subterms. */
if (ATgetType(e) == AT_APPL) {
@ -345,9 +350,14 @@ static Expr evalExpr(EvalState & state, Expr e)
/* Consult the memo table to quickly get the normal form of
previously evaluated expressions. */
NormalForms::iterator i = state.normalForms.find(e);
if (i != state.normalForms.end()) return i->second;
if (i != state.normalForms.end()) {
if (i->second == state.blackHole)
throw badTerm("infinite recursion", e);
return i->second;
}
/* Otherwise, evaluate and memoize. */
state.normalForms[e] = state.blackHole;
Expr nf = evalExpr2(state, e);
state.normalForms[e] = nf;
return nf;

1
testpkgs/infrec/infrec.fix Normal file
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@ -0,0 +1 @@
IncludeFix("infrec/infrec.fix")